Air pump lubricant



Patented July 18, 1944 UNITED STATES PATENT OFFICE AIR PUMP LUBRICANT No Drawing. Application August 13,1940,

Serial No. 352,408

Claims. (Cl. 252-334) This invention relates to lubricants and more particularly to lubricants for air pumps and to methods of lubricating air pumps.

The lubrication of air pumps involves special problems which are not met with in the general field of lubrication. For example, in the ordinary operation of air pumps, the lubricant is subjected to elevated temperatures of the order of SOD-600 F., and the temperature may even reach 1000 F. under extreme conditions' It is an object of this invention to provide an air pump lubricant which will operate efficiently at such elevated temperatures.

Various lubricants have been suggested for air pumps, but none of these has proven entirely satisfactory. In view of the cooling effect of lubricating composition containing water, it has been proposed to utilize emulsions of oil in water in which the emulsifying agent is a metal derivative, such as an alkali metal soap. However, these emulsions had several disadvantages, among which were tendencies to dry out, to gel, to become non-uniform upon standing, and to form deposits upon the parts of the pump during service. If the lubricant dried out to form a tough skin or if a gel formed, the lubricant could not be uniformly fed to the surfaces to be lubricated, thus resulting in excessive wear. Similar dimculties were encountered when the lubricant became min-uniform upon standing. If deposits were formed upon the parts of the pump, frequent cleaning was necessitated in order to insure eflicient operation.

It has now been discovered that the foregoing and other diiiiiculties, heretofore encountered in the lubrication of air pumps, may be obviated by an improved lubricating composition comprising an emulsion of mineral oil in water, in which the emulsifying agent is a soap of an organic base, that is, the reaction product of a monocarboxylic acid and an organic base. The preferred compositions contain an excess of acid over that required to completely react with the organic base.

While triethanolamine stearate has been found to be particularly suitable as the emulsifying agent, various other reaction products of organic bases and monocarboxylic acids are included within the scope of the invention. Commercial mixtures containing major proportions of tri- 'ethanolamine and minor proportions of monoand di-ethanolamine, or either mono-, di-, or triethanolamine alone may be used as the organic base. Other alkyloiamines, such as the propane!- amines, known to be equivalent to the ethanolo acid and oleic acid, may be used, and in general the aliphatic monocarboxylic acids containing at least carbon atoms or mixtures thereof are of utility.

An important element of novelty in the improved air pump lubricants of this invention is that they .form no deposits on the parts of the pump. Prior compositions containing alkali metal derivatives formed deposits on the pump as the result of reactions occurring with oxygen and carbon dioxide at the high temperatures of operation. Alkali metal soaps under these conditions form oxy-compounds and ultimately alkali metal carbonates. The solid deposits of alkali metal carbonates would not be diiilcult to remove 35 in themselves, but these deposits were'intimately associated with deposited carbonaceous matter including free carbon, thus resulting in a deposit which was difllcult to remove. The soaps of organic bases leave no deposit since they are entirely volatile or combustible under the condi-- tions of operation. The improved characteristics, with respect to deposit formation, are obtained irrespective of whether or notthere is present an excess of fatty acid in the lubricant.

Those compositions of the invention containing free acid in substantial amounts have the further advantage that the free acid promotes uniformity in the composition by its emulsifying or solubilizing efiect. The free acid also imparts improved 4o lubricating characteristics to the composition.

According to the invention, it is preferred to add an excess of acid to the organic base so that the free acid in the composition is the same as that reacted with the organic base, but the free acid in the composition may be a diflerent acid. Any of the above-named acids, indicated as suitable for the formationof soaps with the organic bases, may be used as the free acid in the lubricant. However, stearic acid is preferred. In order to obtain the maximum improvement, the

proportion of free acid should be about the same.

as the proportion of organic base soap.

The mineral oil in the lubricant must be chosen with care. Certain high viscosity oils tend to so leave a deposit of carbon on the parts of the pump, and certain low viscosity oils do not afiord suflicient lubrication, resulting in noisy operation of the. air pump. For ordinary operation, the best results have been obtained with a petroleum oil having a viscosity of from 60 to 80 seconds at 210 F. Saybolt Universal. Such an oil may be a single fraction or it may be prepared by mixing a high viscosity oil with a low viscosity oil. For example, a mixture of equal parts of a cylinder stock having a viscosity of 150 seconds Saybolt at 210 F. and a pale oil having a viscosity of- 200 seconds Saybolt at.100 F. has the required viscosity.

An example of the lubricant of this invention which has been found to be particularly suitable.

for the lubrication of air pumps has the following composition:

Per cent by weight Stearic acid 4.0

Cylinder stock (paraflin base; viscosity 150 seconds Saybolt at 210 F.) 7.2

Pale oil (naphthene base; viscosity 200 seconds Saybolt at-100" F.) 7.2 Triethanolamine 0.8 Water 80.8

In the preparation of the lubricant, the stearic acid and petroleum oil are charged in a kettle and heated to about 200 F. The triethanolamine and water are charged in aseco'nd kettle and heated to about 175 F. The mixture in the first kettle is slowly blended with the mixture in the second kettle while agitating. The reaction mixtur is then allowed to cool while agitating over a period of several hours and is withdrawn as finished product. If necessary the mixture may be cooled by circulating water through the jacket of the kettle. The above procedure is given mere- 1y as an example of a suitable method of preparation, but obviously other methods will be apparent to those skilled in the art.

The product obtained as outlined above is a uniform,v dark yellow cream. As compared to the emulsion type lubricants heretofore used, the rate of evaporation of the product of the invention is materially lower. This isan important advantage in that the product will withstand long periods of storage without aifecting its lubricating qualities. Moreover, even after removal of much of the water in the composition, the residue is soft and oily and will readily take up water so that it can be brought to any-desired consistency. No tough, hard skin is formed upon evaporation as was the case with the prior lubricants. The lubricant of the present invention does not corrode or rust metals and is resistant to low temperatures. I

The proportions .of the various ingredients in the composition are quite flexible and may be varied over a fairly wide range, according to the particular properties desired in the finished prod-- water, and the required amount of water to yield ingredients should be present in about the following average proportions:

Per cent by weight (average) Water 80 Mineral oil 15 Soap of organic base 2.5 Free acid 2.5

It has been pointed out in the preceding de-.

the desired consistency can be incorporated at the time of use.

Obviously, many modifications and variations of the invention may be made without departing from the spirit and the scope thereof, and therefore only such limitations should be imposed as are indicated in the-appended claims.

We claim:

1. An air pump lubricant suitable for lubrication at elevated temperatures of the order of 500-1000 F. comprising about 80% water, about 15% mineral oil within the viscosity range of -80 Saybolt Universal seconds at 210 F., about 2.5% triethanolamine stearate, and about 2.5% free stearic acid. I 2. An air pump lubricant suitable for lubricating at elevated temperatures of the order of 500-1000 F., comprising a viscous emulsion of water, a mineral oil within the viscosity range of 60-80 Saybolt Universal seconds at 210 F., a reaction product of an alkylolamine and a carboxylic acid containing at least 10 carbon atoms, and a free carboxylic acid containing at least 10 carbon atoms, said free carboxylic acid being present in approximately equal proportions to the said reaction product of the alkylolamine and carboxylic acid.

3. An air pump lubricant suitable for lubrieating at elevated temperatures of the order of of 60-80 Saybolt Universal seconds at 210 F., and

the reaction product of an 'alkylolamin and a carboxylic acid containing at least 10. carbon atoms.

5. An air pump lubricant suitable for lubrieating at elevated temperatures of the order of 500-1000 F., comprising a viscous emulsion of water, a mineral oil withinthe viscosity range of 60-80 Saybolt Universal seconds at 210 F., triethanolamine stearate and free stearic acid.

GUS KAUFMAN.

KARL UHRIG.

ROBERT S. BARNETT. 

